1. Field of the Invention
The present invention relates to a piezoelectric resonator, a method for adjusting a frequency of the piezoelectric resonator and a communication apparatus and, more particularly, to a piezoelectric resonator in which mechanical vibration of a piezoelectric member is utilized and which piezoelectric resonator is incorporated in an electronic component such as an oscillator, a discriminator or a filter.
2. Description of the Related Art
A conventional piezoelectric resonator, e.g., a piezoelectric resonator 1 such as that shown in FIG. 11, has a base member 2 having a rectangular plate shape and formed of a piezoelectric material, and electrodes 3 provided on the two major surfaces of the base member 2. In the piezoelectric resonator 1, the base member 2 is polarized in the direction of thickness, and a signal is input between the electrodes 3 to excite longitudinal vibration in the base member 2. The piezoelectric resonator 1 arranged in this manner is an unstiffened type in which the direction of polarization and the direction of the electric field differ from the direction of vibration.
A frequency adjustment method for such a piezoelectric resonator is disclosed in Japanese Patent Laid-Open Publication No. 204778/1994. In the method disclosed in this publication, the fact that a resonant frequency of longitudinal vibration is determined by the longitudinal size of a piezoelectric resonator is taken into consideration, and an end surface portion of a piezoelectric resonator is removed to change the longitudinal size of the piezoelectric resonator, thereby adjustably increasing the frequency.
However, if a piezoelectric resonator in which longitudinal vibration is excited is cut for frequency adjustment, stress and frictional heat at the time of cutting negatively influence the piezoelectric resonator. In particular, there is a need to completely recover and remove chips or small particles generated by cutting because piezoelectric materials ordinarily used for piezoelectric resonators contain Pb. This kind of frequency adjustment method also causes negative influences upon other characteristics including the capacitance since portions of the piezoelectric material and the electrodes are removed. In adjusting the frequency by cutting a piezoelectric resonator, it is difficult to control the amount of cutting. Further, the method of cutting an end surface of a piezoelectric resonator does not allow adjustment to reduce the frequency, but only allows adjustment to increase the frequency.